1. Field of the Invention
The present invention relates to a process of producing filaments with an elongation at break of .ltoreq.180% by spinning polymer blends based on polyester or polyamide with an amorphous second polymer at a draw-off speed of .gtoreq.1,500 m/min.
2. Summary of the Related Art
Spinning of polymer blends is known from several publications:
Japanese Patent 56-85420 A (Teijin) describes an undrawn polyamide (nylon) yarn, where an improved productivity is achieved by adding 0.5-10 wt % of a bisphenol polycarbonate.
European Patent No. 35, 796 A (Teijin) describes synthetic fibers, including those made of polyester or polyamide containing 1-15 wt % of a polysulfone polymer having a high glass transition temperature T.sub.g .gtoreq.150.degree. C. The additive remains in a spheroidal form in the matrix and affects the surface structure of the filaments and the fiber friction. The spinning speed is 2000-5500 m/min.
European Patent No. 41,327 B (ICI) discloses fibers of PET or nylon-66 containing 0.1-10 wt % of another polymer with anisotropic properties (LCP grades). The spinning speeds amount to 1000-5000 m/min. A wind-up speed suppression (WUSS, i.e., the properties of the fibre spun from polymer mixture are those that would be obtained from a fibre spun from the non-mixed polymer at lower wind-up speed) is achieved due to the higher elongation at break of the spun fiber and thus higher drawing ratios and a greater increase in productivity.
European Patent No. 80,274 B (ICI) concerns fibers of PET, nylon-66 or polypropylene containing 0.1-10 wt % of another polymer that is present in the melt with an average particle size of 0.5-3 .mu.m and is deformed to fibrils in melt spinning. The spinning speeds are 2000 to 6000 m/min, where a speed suppression (WUSS) of at least 20% is achieved due to the greater elongation at break and the lower birefringence of the (PET) spun fiber, and, thus, higher drawing ratios and increased productivity are achieved. Preferred polymer additives include polyethylene glycol or nylon-66 for PET or polyolefins for nylon-66. The effect is extremely sensitive to production parameters such as throughput, spinning temperature, type of blending and type of extruder. Due to the sensitivity of the process, it is difficult to transfer the process to production facilities of a different capacity, types of equipment, or titer programs.
Japanese Patent 56-91013 A (Teijin) discloses an undrawn polyester yarn, where an improved productivity is achieved by adding 0.5-10 wt % of a styrene polymer. The improvement is due to the increase in elongation at break of the spun fiber at speeds between 850 and 8000 m/min, preferably .gtoreq.2500 m/min, and accordingly higher drawing ratios.
European Patent No. 47,464 B (Teijin) discloses an undrawn polyester yarn, where an improved productivity is achieved by adding 0.2-10 wt % of a polymer of the type --(CH.sub.2 CR.sub.1 R.sub.2).sub.n -- such as poly(4-methyl-1-pentene) or polymethyl methacrylate. The improvement is due to the increase in elongation at break of the spun fiber at speeds between 2500 and 8000 m/min. Higher drawing ratios are achieved accordingly. It is important to achieve a fine and uniform dispersion of the polymer additive by mixing, where the particle diameter must be .ltoreq.1 .mu.m to prevent the development of fibrils. The effect is determined by the interaction of three properties--the chemical additive structure, which hardly allows elongation of the additive molecules, the lower mobility and the compatibility of polyester and additive.
European Patent No. 631,638 B (AKZO) discloses fibers mainly of PET containing 0.1-5 wt % of a 50-90% imidized polyrnethacrylate alkyl ester. The fibers obtained at spinning speeds of 500-10,000 m/min and subsequent drawing have a higher initial modulus. Spinning at very high speeds (such as 8000 m/min) should be possible at conventional thread breakage rates. At speeds up to 8000 m/min, partially oriented fibers are obtained that have not yet been drawn to the final elongation and can be processed to yield textured yarns, for example. In the case of industrial yarns, the effect on the modulus cannot be easily reproduced; the strength achieved is generally lower, which is a great disadvantage for this product. Only drawn yarns have been described for textile applications. The respective undrawn yarns at spinning speeds in excess of 6000 m/min yield an elongation at break of .ltoreq.65.3%, which is not suitable for further processing by draw texturing or stretch texturizing because of the high crystallization associated with this value (boiling shrinkage .ltoreq.6.5%).
One of the goals of spinning polymer blends to synthetic fibers is to obtain a greater elongation at break in the spun fiber at a certain spinning speed than is possible without modification by the added polymer. This permits a higher drawing ratio in production of the final yarn, which should permit a greater productivity of the spinning unit. According to European Patent No. 41,327 B, the gain in productivity to be expected can be calculated by the equation: ##EQU1## where E/E' is the unmodified/modified elongation at break. Reviewing this equation shows that the effect is greatest when the increase in elongation (E-E') is great. However, an excessive elongation and thus a reduced orientation of the spun fiber are not suitable for processing in high-speed stretch texturizing processes.
Another method of increasing the productivity is described by the parameter WUSS .gtoreq.20% in European Patent No. 80,274 B. With a spinning speed at least 20% higher, the same elongation at break is obtained in the spun fiber as at a lower speed with unmodified polymer. However, that publication does not disclose the running behavior at high speeds in the spinning mill or in further processing units or any properties of the final yarns produced there.
Increasing production rate tends to improve the profitability of the manufacturing process. On the other hand, profitability is reduced to a certain extent by production problems and expensive high-speed equipment. The additional cost of the polymer additive has a significant effect, so there is actually a zero point for profitability as a function of the amount added. The market availability of the polymer additive also plays an important role. For these reasons, many of the additives described in the literature are unsuitable for large-scale industrial implementation.
The producer or contractor must take into account the entire production chain and cannot balk at an increase in production in a substep (e.g., in the spinning mill). Follow-up processes must not be impaired. In particular, one of the main goals of this invention is not to limit the further processing conditions in the subsequent steps, but preferably to improve them and to accomplish this despite the increased spinning speed.
Thus, in the prior art a very high elongation at break is achieved for polymer blends also at high spinning speeds that correlate with a great reduction in orientation. Such spun fibers are known to be unstable in storage and cannot be fed or processed at high speeds in friction texturing processes. On the other hand, an elongation of &lt;70% at break at high spinning speeds indicates a high degree of crystallization that reduces the strength achieved in the texturing process. For highly oriented yarns (HOY) using extremely high spinning speeds in the spinning process, an increase in elongation at break is problematical for the mechanical stability of the yarn in textile processing operations such as weaving. The increased elongation reduces the orientation, which in turn results in a lower modulus, which can be regarded as having a negative effect on quality.